London Underground would be faster if it moved more slowly

Transport and traffic networks across London would move more freely and efficiently if the speed of Tube trains was cut, according to a a new study.

Researchers writing in The Journal of the Royal Society Interface calculated that London Underground trains should travel around 1.2 times faster than the average speed of traffic on the roads, so as to minimise congestion and bottlenecks where people move from one transport mode to another. Based on that, and figures published by the BBC, the ideal speed for a tube train would be just 13mph (21kph). Currently, trains run at an average speed of 21mph (33kph).

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It might be natural to assume faster trains would result in a quicker transport network overall, the study found that, due to the decentralised nature of London's underground network, "there is an optimal subway speed in terms of global congestion". The same logic does not apply to dense, highly centralised subway networks such as that found in New York. The study observed that "congestion in central places in New York is so large that introducing an efficient subway system is always better."

In London's case, where the network is more spread out and users are more likely to use multiple modes of transport in a journey, the study calculated that "even when the underground is only 1.25 times faster than the street network, already about 70 percent of the quickest paths are going through the underground." As the number of quickest routes using the tube increases, more people will use it for short-hop journeys, increasing congestion. Faster underground trains also act to create congestion at the ends of lines, further out from the city centre.

The mathematical study analysed and compared transport networks in London and New York with a specific aim of understanding how street and rail networks interact with one another. It concluded that "it is important to consider full multimodal, multi-layer network aspects in order to understand the behaviour of an urban transport system". "Giving exact numbers is a tricky thing, but the fact is that these networks are coupled to each other. Optimising something on one network can bring bad things on another network," senior author Dr Marc Barthelemy told the BBC.

Although the study is purely topographic and doesn't include any passenger data from Transport for London, professor Michael Batty, a planning expert at University College London agreed that "if you join networks together, then you get unanticipated effects. I think the point they're making is well worth considering."